I've seen manifolds glowing orange. 500* is nothing. Likely what is happening, is that when the engine is shut down, the fuel is boiling in the carb bowl. I have a Chevy 283 in my CJ5 that does the same thing. When it's hot, push the gas pedal all the way to the floor and hold it there. Then try cranking it, I'll bet it lights off after a few revolutions. When it fires, take your foot off the gas (obviously). If it really bothers you a lot, you might be able to find a carb isolator. All it is is a really thick gasket to help insulate the carb from heat coming up through the manifold.